The present application relates to an apparatus for preparing a working, processing or machining liquid of an electroerosion or spark erosion machine.
Electroerosion machines typically have a working container filled with a machining liquid in which a workpiece to be machined by electroerosion is immersed. In the case of wire cutting or wire erosion machines the machining liquid consists of deionized water, whereas in the case of countersinking machines it consists of hydrocarbons. Due to the abrasive removal of particles from the workpiece there is a decrease in the cleanness of the machining liquid, so that there is also a change in its electrical conductivity. In order to maintain a desired erosion quality, it is necessary to clean the machining liquid so as to keep the electrical characteristics and cleanness thereof within predetermined ranges. The prior art cleaning devices use in general filters for preparing the machining liquid and those filters have a comparatively large pore diameter. In the case of the large pore sizes of such conventional filters the filtering action is, however, not adequate to maintain the quality of the machining liquid of an electroerosion machine within a desired quality range for a period of several days. However, a reduction of the pore diameter of conventional filters in order to increase the filtration quality leads to a clogging of the filter walls.
It is generally known in the field of filter technology to use membrane filters, which have an extremely small pore cross-section compared with the pore sizes of conventional filters of other types. However, membrane filters have been considered unsuitable for coarse filtering of the concentrate in electroerosion technology because, as a result of the high solids content of the concentrate, it was feared that the membrane filter would rapidly clog.
Therefore, in the preparation of the machining liquid of electroerosion machines, membrane filters have only been used for very specialized functions, but never for cleaning or preparing the concentrates. For example, JP-OS 62-24917 discloses an apparatus for the preparation of the machining liquid of an electroerosion machine, in which use is made of a membrane filter. The known apparatus comprises a container for the machining liquid, which is subdivided into two areas by a cellophane membrane. The first one of the two areas is connected by means of a pump, downstream of which is connected a conventional filter, to the working area of the electroerosion machine, which, by means of a further pump, can be drained into the first area of the container. The second area of the container is connected by means of a yet further pump to an ion exchanger. The ion concentration in the second container area is considerably below the ion concentration in the first container area, so that the ion exchanger can be operated with a low ion density, which is favorable for its operating behavior. In this known apparatus, for the preparation of the machining liquid, a conventional filter is used for filtering the concentrate, whereas a membrane filter is used only for the adjustable reduction of the ion density for a circulation of an ion exchanger.